A map key should tell what the symbols on a map mean what does a small blackened dot usually represent?

= a city

A city, (though not a major one as a major city is represented with a slightly larger dot.)

Usually means a city, town, recognized place, or neighborhood. The key will show what certain things mean on a map. Also, these answers come from the mind of a student from Mrs.Brown's class who...

A city..

city